The grue is a sinister, lurking presence in the dark places of the earth. Its favorite diet is
adventurers, but its insatiable appetite is tempered by its fear of light. No grue has ever been seen
by the light of day, and few have survived its fearsome jaws to tell the tale.

In this culture it is not wise to talk too much good things about anything - especially children,lest some evil spirit steals it. So it is customary to say it is ugly and weak and will surely not survive. Also:
"The man who boasts of his young woman is a fool,
The man who boasts of his wares will get rich."